This invention relates to a remote fluid level detection system. The system uses magnetic detection to determine the fluid level in a confined vessel. Suitably, the invention is utilized with anhydrous ammonia field tanks.
Anhydrous ammonia (NH3) is a substance used in agriculture as a fertilizer because of its high nitrogen content. Typically, anhydrous ammonia is applied to fields in the fall after the crop has been harvested to replenish the nutrients for the next season. The application of anhydrous ammonia involves the use of a field tractor, a field implement that is pulled behind the tractor and a large anhydrous ammonia tank that is pulled behind the implement. This creates a relatively long, train-like configuration of machinery.
Anhydrous ammonia is a multi-phase chemical that, when stored under pressure in the field tank, is in the liquid phase. Upon application, the fertilizer is injected into the topsoil, and it undergoes a phase transformation while percolating through the soil in a gaseous state. Since anhydrous ammonia is a hazardous material, and needs to be stored under pressure, the field tanks are made of heavy gauge steel; much like propane tanks for remote residential use. As a result, fluid level inside the tank is not visible and a special measurement device is needed to indicate fluid level remaining in the tank.
Many existing fluid level sensing systems make use of a magnetic float gauge assembly. Such an assembly comprises an aluminum float-arm that pivots about the center of the tank (See U.S. Pat. No. 2,795,955, incorporated herein by reference). As fluid level changes within the tank, the buoyancy of the anhydrous ammonia affects the position of the internal float. The arm is mechanically coupled via bevel gears to a vertical shaft that runs to the top of the holding tank. Fluctuations in the position of the internal float translate to a small angular rotation of the vertical shaft. To keep the tank completely sealed, a permanent magnet is attached to the top of the vertical shaft. On the outside of the tank, a simple local compass, with fluid level markings, then tracks the position of the internal magnet. In this way, the fluid level of the anhydrous ammonia tank is made visible to the farmer without creating any opportunity for leaks since there are no through-holes or seals needed for the tank gauge to function.
This type of gauge system, however, has many shortcomings. When the farmer is applying the anhydrous ammonia, the fluid level inside the tank is not known because the size and orientation of the gauge face render it completely unreadable from the cab of the tractor. This situation makes it necessary for the farmer to periodically stop application of anhydrous ammonia, get out of the tractor, and walk forty feet back to the field tank to read the small dial on the top of the tank. A standard 1450 gallon anhydrous ammonia field tank is sufficient for only 40 acres of farmland, so this tedious task of determining the fluid level as the tank reaches empty is a recurring annoyance that results in degraded time efficiency.
Another shortcoming of the prior system, is that the total amount of dispensed ammonia is not accurately known until the tank has been emptied. When the tank has been emptied, the farmer can finally approximate the total acreage covered by one full tank, and thus the application rate per acre.
The need exists, therefore, for a means by which fluid level may be known to the farmer on a continuous basis from within the tractor cab during the application process.
The present invention relates to a remote fluid level detection system which provides information to the user, in a wireless fashion, on the fluid level of a towed tank. The present invention is suitably designed for use with a tank containing anhydrous ammonia, but can be practiced with any tank containing fluid and a magnetic float gauge assembly.
Fluid level information is available on a continuous basis as fluid application is occurring. This eliminates the current need to stop application to physically read the existing gauge mechanism on the field tank.
The invention is composed of two electronic modules, a tank module and a display module, that communicate with each other by wireless means, namely a radio frequency transmission.
The tank module is affixed atop the existing mechanical gauge mechanism on a towed field tank, and utilizes a magnetic detection scheme to sense the orientation of a local magnetic field produced by the embedded magnet of the float gauge assembly. The position of the embedded magnet corresponds with the fluid level within the tank.
Due to the hazardous nature of anhydrous ammonia, the application and storage of the fluid is a closely controlled process by various industrial and government agencies. Therefore, a fluid sensing means which would require any modifications to the existing tank would require lengthy testing and approval requirements. The present invention does not require any modifications or removal of any existing hardware and therefore is a completely safe and easy to use fluid level detecting system that does not adversely affect the performance and safety of the original system. The means by which magnetic detection is achieved in the present invention is sufficiently sensitive to eliminate the need for removal or modification of the existing gauge face on an anhydrous ammonia tank.
The tank module physically covers the existing gauge mechanism. A small liquid crystal display on the tank module indicates the percentage of fluid remaining. This liquid crystal display may be incorporated into the tank module at a vertical orientation, to provide much easier viewing of internal fluid level.
The tank module is quickly and easily installed to existing fluid measurement hardware on a tank by the use of a quick-release mechanical system, which captures the head of the existing gauge firmly and without the use of any tools. This allows for the tank module to easily be moved from tank to tank with very little effort and time.
The tank module is designed to accommodate a number of possible mechanical gauge configurations found on a tank, such that various bolt patterns and gauge head geometries will interface equally well with the tank module. The geometric constraints of the tank module limit the orientation by which the invention may be installed to two distinct orientations: an orientation aligned with the magnetic sensing element, and an orientation 180 degrees offset from the magnetic sensing element. In the event the tank module is installed on the existing gauge mechanism 180 degrees offset from the orientation of the internal magnetic sensing element, the control firmware identifies this misalignment and resets the internal origin to compensate for this misalignment, such that the invention will operate equally well in either one of the two mounting orientation possibilities.
Prior fluid level detection gauges utilizing magnetic fields often do so as a means to merely detect low fluid levels or to detect fluid levels at one of several discrete fluid levels. The present invention utilizes a magnetic detection scheme that permits much higher resolution and therefore a much more precise indication of internal fluid level over a continuum between xe2x80x9cfullxe2x80x9d and xe2x80x9cempty.xe2x80x9d The capability of more precisely monitoring fluid levels using this magnetic detection scheme may then be used in conjunction with other inputs to output secondary information that would not have previously been possible.
Within the tank module, a microcontroller based electronic circuit detects the orientation of the magnetic field being generated by the permanent magnet inside the existing gauge mechanism. This magnetic orientation detection is accomplished by utilizing a magnetic sensor. The magnetic sensor is capable of interfacing with the microcontroller within the tank module and reports the orientation of the magnetic field to one degree of precision or better. This allows the microcontroller to locate precisely the position of the embedded tank magnet, and consequently the corresponding internal fluid level. Data stored in an internal look-up table within the tank module microcontroller is referenced to translate the magnetic field orientation reading to a usable fluid level value that corresponds with a percentage of fluid remaining in the tank.
The tank module is equipped with a radio frequency (RF) transmitter that encodes the resulting fluid level data, and transmits it in a wireless fashion to the display module mounted inside the tractor cab. The display module receives the signal from the tank module, decodes the information and utilizes this information for a number of purposes.
Information on the current fluid level can be directly conveyed to the user within the tractor cab via a visible liquid crystal display in the display module. Additionally, a xe2x80x9ctank lowxe2x80x9d audible alert is included in the system to notify the user when fluid level has dropped beneath a certain threshold.
The display module includes a means by which it can interface with the tractor""s electronic groundspeed indicator, thereby providing information to the display module on the tractor""s rate of travel through the field. The display module also permits the user to input information on the size of the anhydrous ammonia field tank and the width of the field implement.
Information from the tank module on current fluid level is combined with information on the tractor""s groundspeed, information on the anhydrous ammonia tank size, and information on the width of the field implement, to provide useful secondary information. The width of the field implement information is multiplied by the tractor""s groundspeed on a time-basis to monitor and store total acreage covered for any given tank. Fluid level information is also monitored and stored on a time basis, such that a corresponding vector can be calculated which approximates the flow rate of anhydrous ammonia to the field. The flow rate is then divided by the corresponding acreage covered to yield a corresponding average application rate per acre.
Manipulating the same information in different ways, and with various conversion constants, allows the invention to display information on the time remaining until tank is empty, number of acres covered per tank and warnings if fluid level drops faster than a set threshold, which would indicate a burst hose or other catastrophic event. The present invention permits this calculation to occur much earlier in the application process, and thus allows the user to compensate for any error between desired application rate and actual application rate. Such displayed data allows the user to compensate for any error between the desired application rate and the actual application rate. The invention, therefore, can lead to significant material savings if these errors in over-application are caught earlier rather than later. Furthermore, the invention can catch under-application errors, which can lead to even greater adverse economic consequences than over-application due to the loss of crop yield.